The accommodation of freight on freight carriers, such as aircraft, requires a reliable power driven conveyor system for moving the freight between stored and unstored conditions. Such power driven conveyors must be capable of moving the freight both laterally and longitudinally within the aircraft for several reasons. One such reason is that the freight may span only a portion of the width of the aircraft. For example, on the main deck of a wide body aircraft, such as the DC 10 or the 747, several freight containers may be placed side-by-side across the width in the aircraft cargo area. The power driven conveyor section is made steerable in order to shift the cargo laterally in the cargo area before transferring it longitudinally down the cargo area. Another reason for providing a steerable conveyor section is that most aircraft cargo areas are accessed through a door in the side of the fuselage. Freight must therefore be conveyed into the cargo area in a lateral direction, turned at a right angle and then conveyed longitudinally into the cargo area in a perpendicular longitudinal direction.
The shipping of cargo is a highly competitive industry. Profits are in large part dependent on the amount of cargo which can be moved in a given period of time. Accordingly, the more cargo which can be loaded on an aircraft, the greater the profit. And likewise, the faster the cargo can be loaded and unloaded, the greater the profit. As the size and weight of the conveyor system has a direct impact on the total weight of freight which can be loaded in an aircraft, as well as the speed with which the loading/unloading operation takes place, the shipping industry is highly receptive to technical improvements in the conveyor art.
Examples of prior art steerable cargo power drive units may be found in the U.S. Pat. Nos. 3,978,975 to Herbes et al, issued Sept. 7, 1976, and 4,589,542 to Steadman, issued May 20, 1986. These references disclose steerable power drive units mounted in association with rollerways in the aircraft cargo area and capable of driving the freight either longitudinally or laterally in the aircraft, as required. The prior art, however, it particularly deficient in that the steerable power drive units comprise large and heavy units which must be partially mounted below the floor surface. That is, a large hole is cut through the floor of the aircraft in order to allow a recessed mounting of the steerable drive unit. It will be appreciated that such a cutting of the floor of the aircraft structurally weakens the aircraft and permanently scars the floor. Furthermore, such units are large, bulky and subsequently very heavy. As weight plays a critical factor in the amount of cargo that can be loaded into an aircraft, the heavy prior art steerable power drive units are deficient.